If you know how to use a simple parametric EQ, you know how to use the Presonus EQ 3 B. Each of the three bands each have the standard parameters of frequency, gain, and Q (bandwidth). There are also buttons for both bypass and a high pass filter at 80 Hz. That is all there is to the unit, so as you can see everything is pretty straight forward. Since it is so easy to use, I don't think that a manual is necessary.
The Presonus EQ 3 B will definitely get the job done as far as sound quality is concerned in home studios, but probably isn't up to par for professional engineers and studio owners to be using. It does have a pretty clean sound, but when compared to top tier pieces of equipment, this really can't touch them. However, if you're looking for a cheap option in terms of EQ in the form of outboard gear, the EQ 3B will get the job done more times than not. It is pretty versatile and can be used on just about anything. While it would never be my first choice for outboard EQ as I generally use the console's EQ, this is a cheap way for home studio owner to get outside of the box EQ.
The price of the Presonus EQ 3 B is the best feature, as it makes it the perfect option for the smaller studio owner looking to get their feet wet with outboard EQ, or simply to get a more realistic sounding EQ than what their plug-ins are offering them. Like I said, this wouldn't be my first choice for outboard EQ, but in terms of models in this price range, this is one of the best on the market. The Presonus EQ 3 B definitely fits in the 'bang for your buck' category...